22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



separation, as well as its possible age difference, may justify tentative 

 recognition. 



While the moderately conservative range in size of M. robustum 

 in Knight beds beneath the Fontenelle tongue of the Green River in 

 southwestern Wyoming is clearly separable from that of the smaller, 

 typical M. chamense size from above the Fontenelle tongue, the 

 somewhat earlier situation in the San Juan Basin is not so clearly 

 resolved. The range in size there is much greater and is said to be 

 continuous so that no logical separation could be made between M. 

 chamense proper and M. terraerubrae. Granger (1915) illustrated 

 this by regarding M. terraerubrae as a subspecies of M. chamense, 

 but this is not strictly tenable unless some ecologic barrier or strati- 

 graphic difference can be shown. With the range in size evident I 

 suspect that there is more than one species represented, not clearly 

 definable in the material represented, or there is a strong potentiality 

 for such a split. 



There is no evidence of a developmental sequence from M. tapia- 

 citis through M. chamense to M. robustum as might be suggested by 

 size, because in about mid-Wasatchian time approximately contem- 

 porary occurrences are known, although the species are not actually 

 found associated. This is further emphasized by the survival of M. 

 chamense into later Wasatchian time than M. robustum. 



THE SKELETON OF MENISCOTHERIUM, WITH NOTES ON 

 PHENACODUS, HYOPSODUS, AND OTHER CONDYLARTHS 



SKULL 



In overall appearance the skull of Meniscotherium is relatively 

 broad across the frontals, and the robust rostrum is approximately 

 equal in length to the more slender cranial portion. The posterior 

 extremity of the tooth row and the orbital constriction across the 

 frontals come very near a mid cross section of the skull. In longi- 

 tudinal profile the dorsal surface is only gently convex to nearly 

 straight. The basilar axes, palatal and basicranial, appear nearly 

 parallel but intersect at a relatively low angle in the least distorted 

 specimens. Notable are the prominence of the postorbital processes 

 of the frontals, the extent to which the squamosal portion of the 

 zygomae flare upward and inward, the backward deflection of the 

 lambdoidal crest and the marked length of the paroccipital processes. 

 Moreover, the cheek teeth are strikingly selenodont, and accompany- 

 ing this the glenoid surface for articulation of the lower jaw is bicon- 

 cave and anteroposteriorly elongate. 



